Observations on Digestion in the Ruminant

Abstract

The results of experiments conducted on goats and sheep by X-rays and by blood-sugar analyses have been considered with the data of other observers and the deductions outlined below have been made. Ingesta, whether liquid or solid, first enter the reticulum and rumen. Heavy matter lodges in the former and light material may enter the same cavity or the rumen. Heavy particles remain in the reticulum for several days until they are broken down, probably by maceration. Light particles move all through the reticulo-rumen at a rapid rate, but the range of movement is least in the posterior ruminal sac. The reticulo-rumen is a mixing and fermentation cavity. Mixing is caused by rhythmical waves of contraction which pass over the reticulum, dorsal sac, ventral sac and posterior sac of the rumen in this order at intervals of 40 to 80 sec., the whole cycle requiring 25 to 40 sec. Onward passage of ingesta from reticulo-rumen is probably due, chiefly to an aspiratory act on the part of the omasum, the leaves of which filter off coarse materials and, by alternating contractions, grind them, while the contraction of the viscus as a whole squeezes the fluid and fine materials into the abomasum. The fundus of the abomasum shows no gross movements, but maintains a steady pressure on its contents, and thus drives them into the pylorus which expels them by peristalsis into the duodenum. Distension of the abomasum probably prevents its overfilling by reflexly inhibiting the movements of the fore-stomachs. The essential factors causing the rejection of the food mass in rumination are (I) thoracic negative pressure produced by sudden descent of the diaphragm and closure of the glottis, (2) relaxation of the circular muscle of the cardia and its dragging forwards by extension of the head and contraction of the longitudinal oesophageal muscle, (3) contraction of the dorsal ruminal sac. A reticular contraction precedes rejection, and swallowing of the remasticated bolus just precedes the succeeding reticular contraction. The fore-stomachs attain adult form at about the 7 month. The vagus is motor and the splanchnics inhibitory to the fore-stomachs. The fore-stomachs contain food after 7 days' starvation. The fasting blood sugar varies from 63 to 86 mg. per 100 c.c., and it rises steadily from the 40th to the 169th hour of fasting. The blood sugar rises slightly but very variably after carbohydrate meals. The inconstancy is related to the X-ray findings, which showed that barium meals may remain in the reticulo-rumen for 60 min. or more, or may pass into the omasum and abomasum within 5 min. after ingestion. The percentage increase in blood sugar after carbohydrate meals is greater in fasted than in non-fasted animals.